Study of Some Growth Indicators of Quercus infectoria on the Side of Forest Roads (Case Study: Shoy Forest in Baneh City)

Extended Abstract Background: Road construction in the forest causes changes in the microclimatic and biological conditions of the roadsides, which lead to positive and negative consequences. Forest fragmentation leads to the creation of smaller habitats and changes in the ecological reactions of the forest, which are different at the distance from the road. These types of changes are called marginal effects. Marginal effects on tree growth indices are different and have been reported from positive to negative in many studies. A review of research records indicates that a few Iranian studies have investigated the marginal effects of forest roads on chlorophyll and carotenoid contents in leaves. Therefore, the current research intends to determine the consequences of forest roads in a part of Zagros forests by examining the marginal effects of forest roads. The contents of chlorophyll a, chlorophyll b, carotenoids, and the specific leaf area index (LAI), as well as the relative humidity of leaves and pollution caused by traffic and the amount of chlorophyll lost in leaves, were evaluated in this research. Methods: To evaluate the positive and negative consequences of road construction, specific LAI, leaf relative humidity, chlorophylls a, b, and carotenoids in leaves, and the amount of leaf pollution caused by dust were studied in the Shoy Forest of Baneh City, Kordestan province. The climate of the region is semi-humid based on the Dumarten climate factor. To carry out this research, a forest road with heavy traffic passing through these forests was selected and three transects were made at a distance of 100 m perpendicular to the road on both sides. At different distances from the road (0, 50, and 100 m), samples of oak (Quercus infectoria Olive.) leaves were collected along the transects. In each transect, the first sample plot of 10 × 10 m was adjacent to the road, and the second and third sample plots were located at distances of 30 and 50 m from the road, respectively. In each plot, leaf samples were collected from all parts of the crown, including infected, damaged, and healthy leaves. The contents of chlorophyll a and b and carotenoids were measured by the Avon method. Oak leaves were taken to the laboratory immediately after collection and their fresh weight was calculated using a digital scale (accuracy of 0.001 g). The surface of the leaves was measured by a leaf surface meter, and the humidity of the leaves was calculated through the weight relationships of the dry and wet weight of the leaves. The total means were compared with the one-way analysis of variance (ANOVA), and the group means were compared using Duncan's test. All statistical tests were performed using SPSS software Ver. 22, and graphs were drawn with Excel software. Results: The marginal effects of road construction on the specific LAI showed that the value of this index decreased with increasing distance from the road, and the highest value was observed at distances of 0 and 50 m from the road. The highest leaf relative humidity was measured at a distance of 50 m from the road, and there was no significant difference at the edge and at a distance of 100 m from the road. No consistent trend was observed in the relative humidity changes, but this variable noticeably decreased on the roadside, which seemed probable. The results of the effect of road construction on the leaf chlorophyll a and b contents showed a decrease in thisvariable with increasing the distance from the road, and the maximum chlorophyll content was obtained at zero distance from the road. Moreover, the highest leaf carotenoids were recorded at distances of 0 and 50 m from the road, and the lowest amount was observed at a distance of 100 m. According to these results, the forest road construction has reduced the light competition between the trees, and those near the road contain more chlorophyll, which can lead to an increase in leaf photosynthesis. The highest contents of chlorophylls a and b were obtained at zero distance (2.01 and 0.97 mg/g of fresh weight, respectively), and carotenoids (0.15 mg/g fresh weight) were maximal at a distance of 50 m from the road, which was not significantly different from carotenoids in the zero distance (0.14 mg/g fresh weight). The results of dust volume caused by the traffic of vehicles showed more pollution of leaves (0.845 g) on the roadside while a leaf contamination level of 0.13 g was recorded at a distance of 100 m from the road. The present findings on the effects of road construction on the amount of chlorophyll lost in leaves showed a significant difference in this variable only at a distance of 0 m from the road, but these differences were not significant at distances of 50 and 100 m from the road. Conclusion: Overall, the marginal effects of forest roads in the investigated area were positive regarding the contents of chlorophylls a and b and carotenoids, as well as the specific LAI, while these effects were negative in terms of pollution. The lost amount of chlorophyll in leaves and the leaf relative humidity index demonstrate the negative consequences of road construction.